[ITK-users] Error encountered when padding: boundary condition is ITK_NULLPTR

Hi all, 

I just performed the segmentation of a vessel from a CT scan and I would
like to use it to mask the abovementioned vessel on the image. In order to
do so I would like to pad the segmentation image which is smaller than the
image from which it has been extracted. 

I get the following error: "PadImageFilter: Boundary condition is
ITK_NULLPTR so no request region can be generated."

My code is the following:

double* voi_bounds = l_import_preprocess.getBounds();
double* seg_bounds = l_import_seg.getBounds();

double x_min = abs(voi_bounds[0] - seg_bounds[0]);
double x_max = abs(voi_bounds[1] - seg_bounds[1]);
double y_min = abs(voi_bounds[2] - seg_bounds[2]);
double y_max = abs(voi_bounds[3] - seg_bounds[3]);
double z_min = abs(voi_bounds[4] - seg_bounds[4]);
double z_max = abs(voi_bounds[5] - seg_bounds[5]);

const int Dimension = 3;
typedef uchar PixelType;
typedef itk::Image< PixelType, Dimension > ImageType;

ImageType::SizeType upper;
ImageType::SizeType lower;

lower[0] = x_min;
lower[1] = y_min;
lower[2] = z_min;

upper[0] = x_max;
upper[1] = y_max;
upper[2] = z_max;

typedef itk::PadImageFilter< ImageType, ImageType > PadFilterType;
PadFilterType::Pointer l_pad = PadFilterType::New();
l_pad->SetInput(l_import_seg.getOutput());
l_pad->SetPadUpperBound(upper);
l_pad->SetPadLowerBound(lower);

typedef itk::ImageFileWriter< ImageType > WriterFilterType;
WriterFilterType::Pointer l_writer = WriterFilterType::New();
l_writer->SetInput(l_pad->GetOutput());
l_writer->SetFileName(logDir.toStdString() + "voi.mhd");
try{
	l_writer->Update();
}
catch (itk::ExceptionObject& err) {
	M_Error(String(err.what()));
}

I also tried to crop the original image to make it fit the segmentation
dimensions but it always is a few pixels smaller than the segmentation image
and I have no idea why. Moreover, this gap is never the same and seems to be
proportional to the segmentation image size.

Why can't I perform the padding of my segmentation image?
Plus, does anybody know why I can't crop the original image without having a
few pixels less than needed?

Thanks in advance,

Marie 



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